1. Field of Invention
This invention relates to a laminating type molded coil and a method of fabricating the same, wherein the coil to be molded is formed on an insulating substrate using a printed wiring technique and wherein the construction of said coil is simple and suitable for mass production.
2. Description of the Prior Art
Various power supply transformers, which comprise one or more coils, are widely used in industrial equipment and domestic appliances. The transformers should have good signal insulating properties and good reliability. In the art, arrangements have been disclosed for forming coils using various techniques. For example see Japan Laid-Open patent No. 58-155,711 and 60-245,208.
FIG. 1 shows conceptually an example of the construction of a prior art molded coil, wherein primary coil 1 and secondary coil 2 are wound in a cylindrical shape and are disposed in a concentric manner in a circumferential direction thereof. The coils may be formed using a printed wiring technique. An insulating layer section 3 is formed by a resin covering the space between the coils 1,2 and the outer periphery thereof and a core is formed about a through hole 4 when a transformer is constructed.
FIG. 2 explains conceptual a method of forming the molded coil of FIG. 1, wherein, first a molding box 5 having a predetermined size and capable of accommodating coils 1,2 is prepared. Then, the coils 1,2 are placed therein concentrically in the circumferential direction thereof. Then, a thermosetting resin, such as epoxy resin is placed between and around the coils, and then heated so as to melt and mold the resin between and about the coils. Then, the resin is allowed to harden, after which, molding box 5 is removed from the core arrangement. Then, the process is completed by a secondary hardening and slow cooling process. The resin is usually in pellet form.
This type of prior art molded coil and method of forming same have the following problems. First, it is not suited for mass production because a separate molding box is needed for each different size of coil, and also, the resin takes a long time to liquify and then solidify. Second, the dimension of the coil cannot be reduced because there must be a definite sized gap between the coils and at the outer peripheries thereof in order for the resin to be placed and hardened in the gaps.